Thermal nonlinear refraction in dye solutions: a study of the transient regime

The efficiency of thermal nonlinear refractive effects in the nanosecond regime is discussed. A single-beam Z-scan and a two-color time-resolved Z-scan experiments demonstrate the influence of the geometric configuration and the pulse duration on the photoinduced index variation. We present a theoretical analysis of thermal-lens formation that takes into account acoustic wave propagation and thermal diffusive effects. It permits us to quantify the index variation during the pulse and to define a new figure of merit for thermal nonlinear refractive effects.